What are the avenues of water entry into the body?

• A. Liquids we drink, water in food, metabolic water from cellular respiration.
• B. Only liquids we drink.
• C. Water produced by photosynthesis.
• D. Water from the air via osmosis.

Answer: (A)

Water entry into the body comes from three main sources: liquids we drink, water contained in the foods we eat, and metabolic water produced during cellular respiration. Drinking supplies water directly to the digestive system, where it is absorbed into the bloodstream. Foods often have high water content, and as they are digested, that water is released and absorbed as well. Metabolic water is generated inside our cells during the oxidation of nutrients; as hydrogen combines with oxygen to form ATP and other byproducts, water is produced and added to the body's water pool. This metabolic water is a small but real contributor to hydration.

The other options don’t fit as primary avenues. Water from photosynthesis is something plants do and isn’t a source of body water for humans. Water from the air via osmosis isn’t a meaningful entry route for hydration in humans—the lungs and skin aren’t reliable paths for absorbing ambient water to meet daily hydration needs in the way drinking and dietary water do.